Hydraulic press with variable retraction for platens



y P. c. POCOCK ET AL 9 HYDRAULIC PRESS WITH VARIABLE RETRACTION FORPLATENS Filed Dec. 8, 1957 3 Sheets-Sheet l INVENTORS A TTORNEYJ.

July 18, 1939. P. C. bcock AL 11 5 3 79 HYDRAULIC PRESS WITH VARIABLERETRACTION FOR PLA'I'ENS Filed Deg s, 1937 3 Sheets-Shet 2, l

Ill

A TTORNE Y5,

1 22 v INVEN7DRSQ Patented July 18, 1939 UNITED STATES PATENT orFicEHYDRAULIC PRESS WITH VARIABLE 'RE- 7 TRACTION FOR PLATENS Paul C.Pocock, Marion, and Victor S. Shaw,

Mount Gilead, Ohio. assignors to The Hydraulic Press Corp., Inc.,Wilmington, Del., a corpora-' tion of Delaware Application December 8,1937, Serial No. 178,772

10 Claims.

Another object is to provide a hydraulic press with means forautomatically applying a relatively large retracting force to the platenat the start of the retraction operation, and subsequently to applyasmaller retraction force.

Another object is to provide a hydraulic press having a plurality ofretraction plunger areas for providing different amounts of retractionforce at different portions of the retraction part of the operatingcycle.

Another object is to provide a hydraulic press with a retraction plungerand an auxiliary retraction plunger, together with means for bringingthe auxiliary retraction plunger into and out of operation, for applyinga larger amount of retraction pressure in a predetermined portion of theretraction stroke.

Another object is to provide a hydraulic press with means responsive tothe attainment of a predetermined pressure upon the retraction stroke toapply an additional retraction force to the press platen.

Another object is to provide a hydraulic press with a double-acting mainplunger having a retraction area and a retraction plunger having anadditional retraction area, together with means responsive to theattainment of a predetermined pressure upon the retraction stroke forapplying both of said retraction areas to the work of retracting thepress platen.

Another object is to provide a method of press-.

ing workpieces, including temporarily applying an additional force toseparate the pressing members at the completion of the working stroke.

In the drawings: l Figure 1 is a central vertical section through oneembodiment of a hydraulic press according to the present invention.

Figure 2 is an enlarged central vertical section through the four-Wayoperating valve shown in Figure 1.

Figure 3 is an enlarged central vertical section through the three-wayauxiliary retraction valve shown in Figure 1.

Figure 4 is an enlarged central vertical section through thepressureresponsiveswitch shown in Figure 1.

Figure 5 is a modification similar to the righthand portion of Figure l,but showing mechanical means for shifting the retraction valve.

Figure 6 is an enlarged vertical section through the retraction valveshown in Figure 5.

Figure 7 is an enlarged vertical section through a modified retractionvalve for use in the circuit 10 of Figure 1, wherein the retractionvalve is shifted by hydraulic means; I

General arrangement In general, the hydraulic press circuit of this 15invention consists of a hydraulic press having a main plunger for movingthe platen upon a working stroke, and a'plurality of retraction plungerareas for retracting the plunger, certain of said areas being insertedin. the circuit during a pre- 20 determined portion of the-retractionstroke in order to apply a greater retraction force during one portionof the retraction stroke than during another portion. Means, such as apressureresponsive switch, and an electrically operated 25 valve areprovided for distributing pressure fluid to the additional retractionplunger area in response to the attainment of a predetermined pressureupon the retraction stroke.

Inperforming certain kinds of pressing oper 3U ations with hydraulicpresses, a considerably larger force is needed in the initial part ofthe retraction stroke thanis subsequently needed for the remainder ofthe retraction stroke. This problem is present in hydraulicmetal-working n3 presses having dies for forming .or drawing metalparts. At the end of the working stroke of such a press the two dies areso firmly engaged with the Work-piece that a considerably greater forceis necessary for separating the dies than for sub- (in sequentlyretracting the platen and main plunger against the forces of frictionand gravity.

Hitherto, when sufficient retraction plunger area has been provided toinsure sufficient force for separating the dies under such conditions,i.) this area has been unnecessarilylargefor use throughout theremainder of the retraction stroke. As a; consequence. there has been aserious loss of speed in the retraction stroke resulting from the largesize of the retraction area .1 and the largev volume of pressure fluidrequired to serve this large retraction arqa. Alternatively. it has beennecessary to provide an additionally high capacity pressure system. suchas an additional hydraulic pump and. motor for slip a;

plying the additional force needed for separating the dies at the startof the retraction stroke, but unnecessary during the subsequent portionof the retraction, Accordingly, with the previous arrangements ofseparating the diesby using a constantrain area on the retractionstroke, much power has been wasted, and unnecessarily large andextensive equipment has been required to supply the pressure fiuidnecessary to apply the requisite retraction force for separating thedies and for maintaining the desired speed of retraction.

By the provision of an auxiliary retraction plunger area, according tothe present invention, and by making it possible to insert and withdrawthis auxiliary retraction plunger area from the stroke, it is possibleto utilize the additional area only for separating the dies. Once thedies have been separated, however the additional area is withdrawn fromthe circuit and the platen is subsequently retracted at a higher speedwithout requiring additional pumping equipment of high capacity.According to the present invention, therefore, the desired speeds ofoperation are maintained with smaller capacity pumping equipment thanhas hitherto been necessary, because the maximum retraction power. isappliedonly during the short portion of the retraction stroke duringwhich it is required. According to the present invention, furthermore,two separate and distinct retraction plunger areas are provided forretracting the main plunger and platen, valves being provided for.selectively admitting pressure to one or both of these retractionplunger areas, as required by the forces demanded at different portionsof the retraction stroke.

Press construction Referring to the drawings in detail, Figure 1 shows apreferred embodiment of the press circuit of thisinvention. In thisembodiment the pressis; provided with a bed H] and head forming bottomand top press members, and interconnected by strain rods |2 having nuts|3 threaded uponthe upper and lower ends, respec- .tivcly. The presshead contains a main cylinder.

|4 having a main cylinder bore l5, within which a main plunger i6 isreciprocable. The latter is provided with a piston head having a forwardor working area l3 and a retraction or return area IS. A packing 20,urged into contact with the plunger |6 by the gland 2|, prevents leakagearound the main plunger l6 at the entrance to the main cylinder bore l5.

Mounted upon the main cylinder is a surge tank 22 for supplying theworking fluid to the circuit. The main cylinder I4 is also provided withan aperture23, within which is inserted a surge valve 24 having a surgevalve member 25 urged upwardly by a coil spring 26 in the direction ofclosingthe passageway through the valve. The surge valve 24 alsocontains aplunger 21, urged upwardly by the coil spring 28 anddownwardly by pressure fiuid supplied thereto in order to forciblymaintain the surge valve member 25 in an open position, directly uponthe return or retraction stroke of the press,- and responsive to thesupplying of pressure fluid to the. retraction cylinders. This surgevalve 24 in itself forms no part of the present invention, and isdisclosed in the Ernst Patent No. 1,892,568 of December 27,

Likewise mounted upon the press-head H is a four-way operating valve,generally designated 29, and a three-way retraction control valve, gen--to the bracket upon the press bed I0.

eraily designated 30. Both of these valves are described subsequently indetail. Secured to the 'main plunger I6 is a platen 3|, suitably guidedand glands for the prevention of leakage.

Die construction The press construction of this invention is adapted tohandle any kind of pressing operation, equipment suitable for metaldrawing being shown purely for purposes of illustration and not by wayof limitation. To this end the platen 3| is provided with a punch 36cooperating with the bore 31 of a die 38 mounted upon the press bed II).In Figure 1 the press is shown as having performed a pressing operationupon a workpiece 39, represented as a deep cylindrical shell of metalclosed at one end. The operation which the press is shown to haveperformed upon this workpiece has consisted in smoothing the outersurface of the workpiece 33 by pushing it through the bore 31 by meansof the punch 36. The die 38 is provided with transverse sockets 40containing pawls 4| urged by springs 42 inwardly to positions engagingthe top of the workpiece after the pressing operation has beenconcluded,

Valve arrangement The four-way operating valve 29 and three-wayretraction control valve 30 are of the piston type, having headsarranged upon valve rods for con trolling the distribution of the fluidpassing therethrough. The four-way operating valve 29 (Figure 2)consists of a casing 44 having a bore 45 and end plugs 46 with apertures41 for the reciprocation of a valve rod 48 with spaced piston heads 49and 50 thereon. Packings 5| and glands 52 revent leakage around thevalve rod 48. The casing 44 is provided with -five annular enlargements53, 54, 55, 56 and 51. The end enlargements 53 and 57 are interconnectedby the passageway'58, terminating in the exhaust port 59. The lower endof the valve rod 48 is threaded, as at 60, for the connection of athreaded collar 6|, into which is inserted the upper threaded end 62 ofthe control rod 63. The latter is provided with adjustable collars 64,and 66, adjustably secured thereto. The upper and intermediate collars64 and 65 are arranged to be engaged by the platen arm 61, secured tothe platen 3|. The lower collar 66, however, is engaged by the arm 68 ofa bellcrank h'and lever 69 pivoted, as at 10, The control rod 63 isguided in its reciprocation by the bored bracket 12 extendingtransversely from the bed Ill.

The three-way retraction control valve 30 (Figure 3) is of similarconstruction to the four-way operating valve 29 and is similarlyprovided with a casing 13, with a bore 14 closed by end plugs 15 withpackings T6, and having four annular enlargements T1 to 80, inclusive.The end enlargements l! and are interconnected by the passageway 8|,terminating in the exhaust port 82, whereas the central enlargements l8and 79 fill terminate in the ports 83 and 84.

Glands 85 similarly prevent leakage around the valve rod 88, whichpasses therethrough. The valve rod 86 is provided with spaced heads 81and 88 for controlling the distribution of the fluid tothe various portsof the retraction control valve 30 according to the position of thevalve rod 86..

On the upper end of the valve rod 86 is a flange 89 serving as anabutment for one end of the coil spring 90, the opposite end of whichengages one of the glands 85 and serves to urge the valve rod 86upwardly. Connected to the lower end of the valve rod 86, as at 9|, isthe armature plunger 92 of a solenoid 93, having a winding 94 which whenenergized serves to pull the armature 92 and valve rod 80 downwardlyagainst the urge of the coil spring 90. The solenoid 93 is mounted upona bracket 95, secured to the press head II.

The winding 94 of the solenoid 93 is energized by the lines 98 and 91leading to the contactsof the switch bars 98' and 99 of the contactorswitch I00. The opposite contacts thereof are connected by the lines IOIand I02 to the power lines I03 and I04, respectively. The contactorswitch I00 is provided with an operating coil I05 connected by the lineI08 to the power line I03, and likewise connected by the line I01 to thecontacts of the switch bar I08 of the pressure-responsive switch I09.From the opposite contact thereof the line IIO leads to the power lineI04. The pressure-responsive switch I09 (Figure 4) is mounted upon thepress bed I0, and is provided with a cylinder bore III, reciprocablyreceiving a plunger II2, the upper end of which is enlarged at II3 toengage one end of a coil spring II4, the opposite end of which engages abrack et H5. The coil spring II4 urges the switch plunger H2 and theswitch rod II6 attached thereto in a downward direction, tending toseparate the switch bar I08 from its contacts. The

pressure-responsive switch I09 is therefore a normally open switch: andcloses only when the I pressure within the cylinder bore III rises to apoint suflicient to overcome the thrust of the coil spring II4. A portII1 serves for the admission of pressure fluid to the cylinder III.

- Hydraulic circuit The hydraulic circuit interconnecting the hydraulicelements previously described is shown in Figure 1. Pressure fluid isprovided by a hydraulic pump I I8 of any suitable type. The pump IIBreceives fluid from the surge tank 22 over the suction line I39, anddischarges pressure fluid through the pressure line I leading to thecentral port I2I of the operating valve 29. The pressure line I20 alsoleads to the upper port 83 of the retraction control valve 30. From theupper 'port I22 of the operating valve 29, line I23 leads to the portI24 in the head of the main cylinder I4. From the lower port I25 of theoperating valve '29, the line I26 leads to the ports I21 in theretraction cylinders 33. A branch I28 leads to the top of the surgevalve 24 for actuating the valve opening plunger 21 upon retractionstroke of the press. From the remaining or exhaust port 59 of theoperating valve 29, the exhaust line I29 runs back to the surge tank 22.i

In the position shown in Figure 2 the operating control valve has beenlifted into its neutral position by the platen arm 61, so that fluidfrom valve 30 is connected by the exhaust line I30.

to the surge tank 22. The remaining port 84 thereof is connected by theline I3I to the lower port I32 in the main cylinder I4 on the oppositeside of the piston head I1 from the head port I24. The spring 90normally urges the valve heads 81 and 88 of the retraction control valve30 into the position shown in Figure 3, wherein the pressure fluid fromthe line I20 normally is entrapped between theheads 81 and 88. When thesolenoid 93 is energized, however, and the valve rod 86 'isdrawndownwardly, the heads 31 and 88 move into positions connecting thepressure line I20 and pressure port 83 with the port 84 and line I3Ileading to the auxiliary retraction area I9 of the main piston head I1.

Operation In the operation of the press circuit of the present inventionthe auxiliary retraction area is ordinarily out of the operatingcircuit, and is brought into the circuit by the retraction control valve30 only when its additional force is necessary. Let it first be assumedthat the various elements of the press circuit are in the positionsshown in Figures 1, 2 and 3. The operator r'emoves the workpiece, whichhas been finished in the previous operation of the press, and places anew workpiece upon the punch 36, above the aperture 31 in the die 30.The operator now shifts the hand lever 89 to the left, causing the arm68 to lift the collar 86 and. control rod 63, thereby from, theretraction cylinders 33, back to the surge tank 22, by way of the lineI26, the operating valve 29 and the line I29. main plunger I6 and platen3| to descend by gravity. The suction thereby createdabove the mainplunger head I1 causes the surge valve member 25 to push against thethrust of the coil spring 28, thereby permitting fluid to pass inrectlythrough the surge valve 24, into the space above the main plunger headI1. This permits the main cylinder to fill rapidly with fluid, withoutdepending upon the fluid supplied thereto by the pump IIB.

When the punch 36 encounters the workpiece 39 and resistance is builtup, the main plunger I6 and platen 3| cease to move by gravity. Pressureis then built up in the head of the main cylinder I4 above the pistonhead I1, this pressure automatically closing the surge valve member 25,assisted by the coil spring 26. The pump H9 thereafter continues tosupply pressure fluid to continue-the pressing operations upon theworkpiece 39 until these operations have been completed. Just before thecompletion of the pressing operation and when the platen has neared thelower limit of its Working stroke, the platen arm 61 engages the collar85 upon the control rod 63,

moving the latter downwardly and shifting the This permits the I offluid.

sure through the branch line I23,from the line I26, enters the surgevalve 24 and urges the plunger 21 thereof downwardly, forcibly openingthe surge valvemember 25. The pressure fluid entering the retractioncylinders 33 engages the retraction plungers 32 and urges the platen 3Iupwardly upon its retraction stroke.

If the force required to separate the punch 36 from engagement with theworkpiece 39 and die 36 does not exceed the normal operating pressurewithin the retraction cylinders 33, the platen 3I rises and proceedsupon its retraction stroke until the platen arm "engages the collar 64and raises the control rod 63. This shifts the valve rod 48 and heads 49and of the operating valve 29 into the neutral position thereof, therebyentrapping the pressure fluid from theline I20 within the operatingvalve 29, and holding the platen 3| in its retracted position.

Meanwhile the space beneath the piston head I1 of the main plunger I6has been in communication with the surge tank 22 by way of the line I3I,which is normally connected to the exhaust line I30 of the retractioncontrol valve.30, as shown in Figure 3. Accordingly as the main plungerI6 moves downwardly upon its working stroke, the fluid beneath the mainpiston head I1 passes directly along the line I3I, through thedetraction control valve 30 and the line I30, into the surge tank 22. Onthe normal return or retraction stroke, as described above, the fluidpasses from the surge tank 22, along the line I30, through theretraction control valve 30 and line I3I, into the space beneath themain piston head I1, filling this space with the proper amountAccordingly, under normal operating conditions, the auxiliary retractionarea I9 on the under side of the main piston head I1 has no effect uponthe speed or force of the main plunger I6, and absorbs none of thepressure fluid deliv-= within the retraction cylinders 33 and istransmitted along the line I33 leading tothe cylinder III of thepressure-responsive switch I09. At a predetermined pressure suflicientto overcome the thrust of the, coil spring II4 the plunger H2 rises andcauses theswitch bar I08 to engage its contacts, closing the circuitbetween the lines I I0 and I01, thereby energizing the operating coilI05 of the contactor switch I00. The switch bars 93 and 99 thereof thenclose upon their contacts, closing the circuit between the lines IM and91, and also between the lines I02 and 96, respectively. winding 94 ofthe solenoid 93, causing the armature 92 thereof and valve rod 66 of theretraction control valve 30 to be drawn downwardly. overcoming thethrust of the coil spring 90.

When this occurs the valve.heads 81 and 88 are shifted so that thepressure line I20 now communicates with the line I3I leading to thelower part of the main cylinder bore I5. Accordingly, pressure fluid nowpasses from the pump II8, along the line I20, through the retractioncontrol valve 30 and along the line I3I. through the port I32, into thespace beneath the auxiliary retraction area I9 of the main piston headI1. At the some time the lower valve head 88 closes the connectionbetween the line I3I and thee);- haust line I30 leading tothc surge tank22v The pressure fluid passing into the lower part of the This energizesthe main cylinder bore I5 engages the auxiliary retraction area I9 ofthe main plunger I6, and

adds this area to the area of the retraction plungers 32, therebyincreasing the force available for lifting the platen 3I and separatingthe punch 36 from the workpiece 39 and die 30.

As soon as the punch 36 has been loosened from its engagement with theworkpiece 39, the force required to retract the punch 36 and platen 3|greatly diminishes and accordingly the pressure in the retractioncylinders 33 drops. This pressure drop is transmitted along the line I33to the cylinder III of the pressure-responsive switch I09, permittingthe plunger II2 thereof to move downwardly under the urge of the coilspring I I4, separating the switch bar I03 from its contacts and openingthe circuit between the lines I01 and H0. This deenergizes the operatingcoil I05 of the contactor switch I00, opens the circuit between itsswitch bars 96 and 99 and their contacts, and deenergizes the lines 96and 91. The consequent deenergization of the solenoid 93 permits thecoil spring 90 to move the valve rod 86 of the retraction control valve30 upwardly to its original position, cutting off the further flow ofpressure fluid from the line I20 to the space beneath the auxiliaryretraction area IQ of the 'main plunger I6, and opening the latter to asupply of pressure fluid, reaching it by way of the exhaust line I30,the retraction control valve 30 and the line I3I.

With the auxiliary retraction area I9 thus removed from the circuit, thetemporary slowing down of the platen 3I, due to its presence, is endedand the platen 3I continues to move swiftly upward, under the influenceof the retraction plungers 3I alone. When the platen arm 61 engages thecollar 64 and shifts the operating valve rod 48 to its neutral position,the pressure fluid from the line I20 is again entrapped between thevalve heads 49 and 50, and the main plunger I6 is held in a stationaryposition until the control rod 63 is moved upwardly to start anotherworking cycle.

In the circuit shown in Figure l the manually operated lever 69 is shownfor simplifying the disclosure. It will be understood, however, that thefour-way operating valve 29 may be shifted by other means, such as byany suitable electric or hydraulic arrangement. Similarly, theretraction control valve 30 may be shifted by means of manual orhydraulic means in order to insert and remove the auxiliary retractionplunger area from the circuit. It will also be understood that thesevalves may be shifted mechanically in response to movement of anysuitable portion of the press. In place of the spring 90, other suitablemeans, such as a pressure cylinder, may be used for returning the valverod 86 of the retraction control valve 30 to its upper position.

The modification shown in Figure 5 provides mechanical means forshifting the retraction control valve 30. The valve 30 is generallysimilar to the valve 30 in Figure 1, except that the spring 90 and theflange 89 are omitted. The valve rod 86, however, is connected to acontrol rod I36 by means of the connection I35, and is guided at itslower end by a lug I31 upon the bed I0 of the press.

Extending laterally from the platen 3I is a platen arm I38. arranged toengage coil springs I39 and I40, mounted respectively above and belowthe platen arm I38 and positioned by means of adjustable collars MI andI42, respectively The upper spring I39 is provided to permit the platen3I-to continue to move upwardly after it has shifted the valve" to itsuppermost position wi'thout causing damage to the control rod I36 or theparts actuated thereby. This provision is made because the'stroke of theplaten CM is greater than the stroke of the valve 30.

w The lower spring I40 serves to move the control III) rodl36 and valverod 86 do'wnwardlywhen the spring I49 is-engaged by the platen arm I36on the downward stroke of the platen.

In adjusting the press for-operation, the collar I42 is moved along thecontrol rod I36 into such a position that the spring I40 will be engagedby the platen arm I38 to shift the control rod I36 downwardly when theplaten 3I nears the lower limit of its stroke. In this manner theauxiliary return area I5 is caused to be opened to the entranceof'pressure fluid by way of the valve'30 as soon as the return stroke ofthe platen 3| is started by admitting'pressure fluid to the lines I26and I28, in response to the operation of the four-way operating valve29. The upper collar MI is adjusted during the setting-up operations ofthe press to such a position along the control rod I36 that the latterwill be moved upwardly when the platen "3| has returned a sumcientdistance on its return stroke to-free the workpiece from the punch. I Atthat point the platen arm I38 engages the'coil spring I39,'and thelatter movesthe collar HI and control rod I36 upwardly, together withthe valve rod 86, shifting the valve 30 and shutting off the auxiliaryretraction area l9 from pressure fluid. In this manner theauxiliaryretraction area I9 is removed from service at a predeterminedpoint on the return stroke of the platen 3|.

In the modification shown in Figure '7, the valve 30 as a whole issimilar to that of Figure I and has a similar coil spring 90. The upperend of the valve rod 86, however, is threaded, as at I43, and providedwith a nut I44 and locknut I45, whereby the force of the spring 99 maybe adjusted. On the lower end of the valve rod 86 I is a piston headI46, mounted for reciprocation in a cylinder I41, threaded as at I48into a threaded flange I49 serving to close the lower end of the valvecasing 13. The upper end of the cylinder I41 communicates, through aport I50, with a conduit I33, whereas the lower end of the cylinder isprovided with a port I5I, communicating with a conduit, I52, whichhas adrain line leading back to the surge tank 22 for draining away fluidwhich escapes past the piston I46. The conduit I33 is connected to thereturn pressure fluid line I26 and is the same conduit as the conduitI33 employed for actuating the pressure switch I09 in Figure 1.

In the operation of the'modiflcation shown in Figure 7 the four-wayoperating valve 29 is shifted so as to admit pressure fluid into thelines I26 and I28 for retracting the. platen 3| by means of pressurefluid admitted to the retraction cylinders 33. The resistance to thewithdrawal of the punch occasioned by the friction between the punch andthe workpiece causes pressure to be built up within the retractioncylinders 33, and this pressure is transmitted along the conduit I33into the chamber above the piston head I46 in the cylinder I41 (Figure'7) When this pressure becomes sufficiently great to overcome the thrustof the coil spring 90, it shifts the piston head I46 and valve rod 86downwardly,"shifting the valve heads 81 and 86 for admitting pressurefluid from the line I26 and the line I3I, leading through the port I32to the auxiliary retraction area I9 the conduit I20.

of the main plunger I6. As soon as the punch is Heed from engagementwith the workpiece by the force of the auxiliary retraction area I9added to the effect of the retraction plungers 32, the pressure withinthe retraction line I26 drops. The consequent drop in the line I33permits the spring 90 to shift the valve heads 8'1 and 88 upwardly,thereby cutting off the auxiliary retraction area I9 from the supply ofpressure fluid in The press platen 3| thenceforth continues itsretraction stroke under the influence of the retraction plungers 32alone.

It will be understood that we desire to comprehend within our inventionsuch modifications as come within the scope of the claims of the invention.

Having thus frilly described our invention, what we claim as new anddesire to secure by Letters tracti'on stroke of said main retractionmeans for temporarily amplifying the force of said main retractionmeans.

2. In a hydraulic press circuit, a platen, a main plunger connectedthereto, main retraction means for retracting said mainplunger,auxiliary retraction means selectively insertible in said circuit duringa minor part of the retraction stroke of said main retraction means fortemporarily amplifying the force of said main retraction means, andmeans responsive to the attainment of a predetermined pressure in saidmain retraction means for rendering said auxiliary retraction meansoperative.

3. In a hydraulic press circuit, a platen, a main plunger connectedthereto, a main retraction plunger connected thereto, an auxiliaryretraction plunger area, and a valve for selectively admitting pressurefluid to said auxiliary retrac tion plunger area during a minor part ofthe retraction stroke of said main retraction plunger for temporarilyamplifying the force of said main retraction plunger.

' 4. In a hydraulic press circuit, a platen, a main plunger connectedthereto, a main retraction plunger connected thereto, an auxiliaryretrac tion plunger area, a valve for selectively admitting pressurefluid to said auxiliary retraction plunger area during a minor part ofthe retraction stroke of said main retraction plunger for temporarilyamplifying the force of said main plunger, and means responsive to theattainment of a predetermined pressure in said main retraction plungerfor shifting said valve to admit pressure fluid to said auxiliaryretraction plunger area.

6. In a hydraulic press circuit, a platen, a main plunger connectedthereto, a main retraction plunger connected thereto, an auxiliaryretrac tion plunger area, a valve [or selectively admitting pressurefluid to said auxiliary retraction plunger area during a. minor part ofthe retraction stroke of said main retraction plunger for temporarilyamplifying the force of said main retraction plunger, electrical meansfor shifting said valve, and means responsive to the attainment of apredetermined pressure in said retraction plunger area for energizingsaid electrical means to shift said valve to admit pressure fluid tosaid auxiliary retraction plunger area.

7. In a hydraulic press circuit, a platen, a main plunger connectedthereto, a main retraction plunger connected thereto, an auxiliaryretraction plunger area, a valve for selectively admitting pressurefluid to said auxiliary retraction plunger area during a minor part ofthe retraction stroke of said main retraction plunger for temporarilyamplifying the force of said main retraction plunger, a tank forsupplying fluid to said circuit, said valve being normally positionedfor maintaining communication between said auxiliary retraction plungerarea and said tank, and means responsive to the attainment of apredetermined pressure in said retraction plunger for shifting'saidvalve to admit pressure fluid to said auxiliary retraction plunger areaand cut of! communication thereto from said tank.

8. In a hydraulic press circuit, a platen, a main plunger connectedthereto, main retraction means tor retracting said main plunger,auxiliary retraction means selectively insertable in said circuit duringa minor part of the retraction stroke of said main retraction-means fortemporarily amplifying the force of said main retraction means, andmeans responsive toa predetermined motion or said platen for withdrawingsaid auxiliary retraction means from the circuit.

9. In a lwdraulic press circuit, a platen, a main plunger connectedthereto, main retraction means for retracting said main plunger,auxiliary retraction means selectively insertable in said circuit duringa minor part of the retraction stroke of said main retraction means fortemporarily amplifying the force of said main retraction means, andhydraulically-actuated means responsive to the attainment of apredetermined pressure in said main retraction means for renderingoperative said auxiliary retraction means.

10. In a hydraulic press circuit, a platen, a main plunger connectedthereto, main retraction means for retracting said main plunger,auxiliary retraction means selectively insertable in said circuit duringa minor part oi the retraction stroke of said main retraction means fortemporarily amplifying the force of said main retraction means, andhydraulically-actuated means responsive to the attainment of apredetermined pressure in said main retraction means for renderingoperative said auxiliary retraction means and responsive to a pressuredrop below said predetermined pressure for rendering inoperative saidauxiliary retraction means.

PAUL C. POCOCK. VICTOR 8. SHAW.

